What is a gage repeatability and reproducibility (R&R) study?

A gage R&R study helps you investigate:
  • Repeatability—How much variability in the measurement system is caused by the measurement device.
  • Reproducibility—How much variability in the measurement system is caused by differences between operators.
  • Whether your measurement system variability is small compared with the process variability.
  • Whether your measurement system is capable of distinguishing between different parts.

For example, several operators measure the diameter of screws to ensure that they meet specifications. A gage R&R study (Stat > Quality Tools > Gage Study) indicates whether the inspectors are consistent in their measurements of the same part (repeatability) and whether the variation between inspectors is consistent (reproducibility).

Examples of repeatability and reproducibility

Repeatability and reproducibility are the two components of precision in a measurement system. To assess the repeatability and reproducibility, use a gage R&R study (Stat > Quality Tools > Gage Study).

Repeatability
Repeatability is the variation due to the measurement device. It is the variation that is observed when the same operator measures the same part many times, using the same gage, under the same conditions.
Operator 1 measures a single part with Gage A 20 times, and then measures the same part with Gage B.

The solid line is the measurements from Gage A. The dashed line is the measurements from Gage B. Gage A has less variation, so it is more repeatable than Gage B.

Reproducibility
Reproducibility is the variation due to the measurement system. It is the variation that is observed when different operators measure the same part many times, using the same gage, under the same conditions.
Operators 1, 2, and 3 measure the same part 20 times with the same gage.

The three lines are the measurements from Operator 1, 2, and 3. The variation in average measurements between Operator 1 and 2 is much less than the variation between Operators 1 and 3. Therefore, the gage's reproducibility is too low.

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